High-frequency multiplex signaling system



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ATTORNEY l Patented Oct. 6, 1925o STATES EH C LLOYD ESPENSCHIED, OF HOLLIS, AND HERMAN A. AFFEL, OF BROOKLYN, NEW YORK,

ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, .A CORPORA- TION 0F NEW YORK.

HIGH-FREQUENCY MITLTIPLEX. SIGNALING- SYSTEM.

Application filed September 30, 1919.

To all whom t may concern Be it known that we, LLOYD EsrENscHinD and HERMAN A. AFFEL, residing at I-Iollis and Brooklyn, in the counties of Queens and Kings and State of New York, respectively, have invented certain Improvements in High-Frequency Multiplex Signaling Systems, of which the following is a specification.

This invention relates to a high frequency multiplex signaling system and more particularly to a translating' circuit arrangement associated with theterminal circuit of such systems whereby the received carrier oscillations maybe reamplified by a re-entrant or feed-back connection associated with the translating circuit. In the multiplex signaling system in which the oscillations of carrier frequency are transmitted simultaneously with the'oscillations of one of the modulated bands of frequencies based upon the carrier frequency it is desirable to amplify at the receiving end the oscillations of carrier frequency relatively more than those embraced within the side band.

fthe undesired components. It is the object Serial No. 327,397.

tion toa terminal circuit having a translating circuit individual to the transmitting and receiving circuits. In Figure I, L1 represents a low frequency signaling circuit related to the terminal circuit by means of transformer T1 and balanced by the network N1. The high frequency signaling circuit L2 is related to the terminalcircuit by transformer T2 and balanced by the network N2. This terminal circuit is of the well known 22 type having incoming and outgoing sides, the incoming side being so connectedl as to impress modulated high frequency received oscillations and carrier currents upon the translating circuit, and the outgoing side being adapted to impress signaling currents upon the translating device from whence they pass to the line L2. The incoming side has therein a high frequency band, filter F2 and a low pass filter F3. In a similar manner the outgoing side has associated therewith a low` pass filter F1 and a high frequency filter F4. Both incoming and outgoing currents are impressed upon the translating circuit by transformer T3 and are transmitted from the output side of the translating circuit by a transformer T4. This translating circuit has therein a single translating device adapted to amplify, modulate and detect the impressed Q'iiof this invention to reamplify the oscilla- Jitions of carrier frequency in the translating jic-ircuit and to use these reamplified carrier lloscillations in the translating circuit in order? `,currents Extending froml the output side of the translating circuit4 to its input side is a feed-back or re-entrant connection having therein resonant circuits 2 and l, which are sharply tuned to carrier frequency.

to effect the modulation and demodulationt, of the impressed currents. "i This invention will be more fully understood from the following description when read in connection with the attached drawing, of which Figure 1 shows the application of the invention to a terminal circuit having a translating circuit common to both the transmitting and receiving paths, in which amplification, modulation and detection are performed by a single tube. 'Figure 2 shows the application to a terminal circuit having a common translating circuit in which amplification is performed by a device separate from the modulator and detector, and Figure 3 Shows the applica- This connection serves to permit the passage of oscillations of carrier frequency from the output side of the translating circuit to the input side, whereby these oscillations may be reamplified and impressed upon the translating device simultaneous with the impressed currents.

The mode of operation of the circuit in which this invention is embodied is as follows: Low frequency signaling currents in the circuit L1 will be ltransmitted by the transformer T1 to the outgoing side of the translating circuit passing through the low pass filter F1. These low frequency currents are impressed upon the input side of the translating circuit by means of the transformer T3 which is adapted to transmit efliciently both loW frequency and high frequency currents. The low frequency current impressed upon this device serves to modulate therein the high frequency currents of carrier frequency received over the line L2 from a source at the other end of the said line. The mode of transmission of the oscillations of carrier frequency will be clearly set forth hereafter. The modulated high frequency oscillations will pass through the high frequency7 band filter F4 and over the transmission line L2 to the terminal circuit at the opposite end of the side line. The filter F2 is a high frequency band filter adapted to pass oscillations of those frequencies lying Within a certain band of frequencies 'based upon the carrier frequency and to suppress the other frequencies based upon the same carrier frequency. The. terminal circuit at the opposite end of the line L2 is adapted to transmit the oscillations of the carrier frequency and also oscillations of those frequencies lying Within one of the side bands. These oscillations will be impressed upon the incoming circuit by the transformer T2 and passing through the band filter' F2 Will 'be impressed by means of the transformer T3 upon the translating circuit. The oscillations of carrier frequency which pass through the translating device are fed back over the re-entrant circuit 2 1 between the output and input sides of the translating circuit, and are amplified thereby. The circuit 2 1 is sharply tuned to be resonant at the carrier frequency thereby preventing the feeding back of other frequencies. By adjusting the translating circuit the oscillations of carrier frequency may be given the desired degree of amplification. The resulting detected currents Will be impressed by the transformer T2 upon the in oming low frequency side of the terminai circuit, and since these currents are of low frequency they will pass through the loW pass filter F3 and be impressed upon the loiv frequency signaling circuit L1.

Figure 2 shows another form in which this invention may be applied to a carrier system in Which the terminal circuits are provided With a single translating circuit common to both the transmitting and receiving paths of the said circuit. In the figure L1 represents a low frequency signaling circuit connected With the four-Wire terminal circuit A by means of the transformer T1. The high frequency side of this terminal circuit is connected with the branch high frequency line L2 by transformer T2. B represents another four-wire terminal circuit having the low frequency line L3 connected thereto by the transformer T3. The high frequency side of the circuit B is connected With branch transmission line L4 by transformer T4. A main transmission line ML connects the two terminal circuits. The translating circuit of the terminal A embodies an amplifier A1 which is adapted to oscillate at carrier frequency by means of a feed back connection. The output side of this oscillating amplifier is connected with the input side of a balanced modulating and demodulating device HD1 which is so designed as to suppress the amplification components of both the high frequency and lou7 frequency currents impressed upon the said device. The translating circuit of the terminal circuit B is also equipped with an amplifier having a feed back connection which is designed to re-amplify oscillations of carrier frequency impressed upon it. The output side of this amplifier A2 is connected with the input side of a balanced modulating and demodulating device MD2 Which is of a type similar to MB1. In the operation of the circuit shown in Figure 2 low frequency signaling currents arising Within the line Ll Will pass through 10W frequency filter F1 and be impressed upon the amplier A1 by transformer T1. The amplified currents on the output side of A1, together with the unmodulated carrier frequency arising from the oscillating circuit will be impressed upon the modulating and demodulating device MDI. The modulated high frequency oscillations will be impressed upon the output side of the circuit A by transformer TG and will pass through the high frequency band filter F2 and will be transmitted over the circuits M2, ML, Ll to the terminal circuit B. Simultaneous With the transmission of these modulated oscillations the unmodulated carrier frequency set up by the oscillating amplifier Al Will be impressed upon the input circuit 1 of the terminal circuit A, and Will pass through the band filter F3 which is designed to transmit also the carrier frequency and will be transmitted over the circuits L2, ML, and L4 to the terminal circuit B. The transmitted side band and the carrier frequency Will pass through the band filter F4 and will be impressed by the transformer T7 on the amplifier A2. Since the feed back connection is tuned to carrier frequency, oscillations of this frequency may be re-amplified the desired amount and impressed together with the side band upon the input side of the translating device MD2. The low frequency signaling current resulting from demodulation will pass through the low frequency filter F5 into the circuit L3, and will actuate the signaling apparatus associated therewith. i The loW frequency signaling currents set up in the line L3 to be transmitted will pass through the low frequency filter F6 and Will be impressed upon the amplifier A2. These low frequency currents will be amplified thereby, and together With the reamplified carrier frequency will be impressed upon the modulating and demodulating device MD2. The modulated high frequency oscillations resulting therefrom will pass through the band filter F 7 and over the circuits L2, ML, and L2 to the terminal circuit A. The frequencies of the band which the filter F3 is designed to transmit will pass therethrough and will be inipressed upon the amplifier A1. These frequencies, together with the modulated carrier frequency generated by the oscillating carrier A1 will be impressed upon the translating device MD1 and the low frequency signaling currents resulting from demodulating will pass through the low frequency filter F8 into the low frequency line L1 and will actuate the signaling apparatus associated therewith. From the foregoing it will be seen that by means of the arrangement shown in Figure 2, the unmodulated oscillations of carrier frequency may be transmitted from one terminal circuit to its cooperating terminal circuit at the opposite end of the line, and by means of a feed back connection associated with the amplifier in the translating circuit and tuned to carrier frequency the transmitted carrier frequency may be re-amplified to any degree desired and used for the purpose of demodulating the received oscillations or to serve as the carrier for low frequency signaling currents to be transmitted. By this arrangement the identity of frequency of the carrier at the two cooperating terminals is assured and amplification of the carrier frequency and of the frequencies in the received side band may be effected.

Figure 3 shows a two way terminal circuit having a modulating and a detecting device connected with the transmitting and receiving paths respectively. In this figure Ll represents a low frequency signaling line and L2 a line for the transmission in each direction of high frequency signaling currents. The line Ll is related to the terminal circuit by the transformer T1 having a network N1 associated therewith adapted to balance the line L1. The line L2 is related to the terminal circuit by means of the transformer T2 having associated therewith the net work N2 adapted to balance the line L2. In the transmitting side of the circuit is the low pass filter F3 and the high frequency band filter F4, and likewise in the receiving side of the circuit are the low pass filter F1 and the high frequency band filter F2. Associated with the transmitting path is a translating circuit Ml which has associated with it a re-entrant circuit which is adapted to oscillate at the carrier frequency and thereby to serve as the generator of oscillations of that frequency. In the receiving side of the circuit is a translating circuit D1 which has associated therewith a re-entrant circuit which is sharply tuned to the carrier frequency, and is adapted to re-amplify oscillations of carrier frequency which arc impressed upon the translating circuit D1 together with the oscillations of the side band frequencies. This invention will be better understood from the following description of its mode of operation:

Low frequency signals set up in the line Ll will be impressed upon the transmitting circuit l and passing through the low pass filter F3 will be impressed upon the modulating circuit M1. These signaling currents will modulate the high frequency oscillations set up within the circuit M1 by the ire-entrant connection and the modulated high frequency oscillations resulting therefrom will be transmitted to the circuit 2. The filter F2 may preferably be designed to transmit one of the side bands and to suppress the other side band, and the carrier frequency. The oscillations of the transmitted side band will be impressed upon the line L2 by the transformer T2 and will be transmitted to the other terminal of the transmission line. The high frequency band filter inthe transmitting path of the terminal circuit at the other end of the line L2 may be assumed to be of a type that is designed to transmit the carrier frequency together with one of the side bands. Therefore oscillations of both the carrier frequency and of the side band frequencies will be received over the line L2 will be impressed by the transformer T2 upon the receiving circuit 3. These oscillations will pass through the high frequency band filter F2 and be impressed upon the detecting circuit D2. Since the re-entrant circuit associated with the detecting circuit is tuned to the carrier frequency, oscillations of that frequency will be re-amplified thereby to a greater degree than the oscillations of the side band frequencies. This amplified cai'- rier current demodulates or detects the oscillations of the side band and the resulting detected current passes through the low pass filter' F1 to the low frequency signaling circuit L1. it will be apparent from the foregoing description that the arrangement shown in Figure 3 provides means for the selective amplification of the carrier current, which is received simultaneously with the side band currents7 and for using this amplified carrier current to detect the 0scillations of the side band.

By re-amplifying selectively the oscillations of carrier frequency the quality of the detected currents is improved by causing the desired components of demodulation to be large compared with the undesired components. The desired components are those representing modulation between the Carrier supply and the band of frequencies representing the side band while the undesired components of demodulation are those representing modulation between the component currents within a side band or between two opposite side bands. By making the carrier oscillations supplied to the detector or demodulator large in comparison with the side band oscillations, the components of demodulation are similarly large compared with the components representing cross modulation between the side band currents. The practical value of this selective amplificationof the carrier employed at the receiving end permits of a reduction in the magnitude of the oscillations of carrier frequency transmitted from the sending end resulting in conserving energy which is im- Vportant in the case of radio-transmission,

and further resulting in a reduced load upon repeaters, which is advantageous in connection with wire carrier current transmission.

Although this invent-ion has been shown as embodied in a particular form, it is apparent that it is capable of embodiment in other and different forms within the scope of the appended claims.

What is claimed is:

l. The method of modulating oscillations in a system characterized by means for the conversion of low frequency variations into high frequency oscillations which consists in simultaneously impressing the low frequency variations and umnodulated carrier oscillations upon a translating circuit, regeneratively amplifying the said carrier oscillations, and simultaneously modulating the said amplified carrier oscillations by the low frequency variations, and transmitting the said modulated oscillations.

2. The method of demodulating oscillations in a system characterized by means for the conversion of high frequency modulated oscillations into low frequency signaling variations, which consists in simultaneously impressing the said modulated high frequency oscillations and unmodulated carrier oscillations upon a translating circuit, selectively amplifying the said carrier oscillations1 impressing the amplified carrier oscillations and the modulated high frequency oscillations upon a detecting device, and transmitting the resultant low frequency variations.

3. The method of modulating and demodulating oscillations in a system characterized by means fo-r the conversion of low frequency variations into high frequency oscillations and vice versa, which consists in simultaneously impressing low frequency variations, modulated high frequency oscillations, and unmodulated carrier oscillations upon a translating circuit, selectively amplifying the said carrier oscillations, impressing the said variations and said oscillations upon a modulating and demodulating device, and transmitting the modulated high frequency oscillations and low frequency variaions resulting from the modulation and demodulation of the said variations and modulated oscillations by said carrier oscillations.

4. In a signaling system, the combination with an input circuit having sources of currents of different frequencies 4connected therewith of an output circuit, a translating circuit having a thermionic vacuum tube connected therewith adjusted to modulate and amplify voltages impressed thereon, and having a feed-back connection between the output and input sides of said tube selective to a particular frequency whereby the regenerative ampliiication of the voltage of the particular frequency may be effected.

5. In a signaling system, the combination with a. thermionic vacuum tube adapted to modulate and amplify voltages impressed thereon, of a source of carrier frequency, a source of di'erent frequency whereby said carrier frequency may be modulated, an input circuit for impressing voltages of said frequencies upon said vacuum tube, an output circuit, and a reentrant feed-back circuit between said output and input circuits tuned to carrier frequency whereby the regenerative amplification of the said carrier frequency may be effected.

6. In a signaling system, the combination with a thermionic vacuum tube adapted to demodulate and amplify voltages impressed thereon, of a source of carrier frequency, a source of modulated carrier frequency to be demodulated by the said carrier frequency, an input circuit for impressing voltages of said frequencies upon said vacuum tube, an output circuit, and a reentrant feed-back circuit between said output and input circuit selective to the carrier frequency whereby the regenerative amplification of the said carrier frequency may be effected.

7. In a signaling system, the combination with a lowfvrequency transmissionuline, of a high frequencyN transmissionliI/ie, a fquwire circuit cqnnectiiig"tbgether said trans-v. mission lines, ailtransglatingcircuit having a n'lodulating and amp]ifyingYM device connected with said four-wire `circuit and arranged to have the low frequency and high frequency currents impressed thereon, the said translating circuit having a feed-back connection tuned to a definite frequency whereby currents ofv that frequency may be reampliied.

. irs@ In a signaling system, the combinatioim with a transmittingcircuit, of aA receiving circuit, a fonrvfrreH circuit connected with 25 said transmittiig'andeceiving circuits and balanced with respect thereto, a translating circuit havingamplifying and olerrio'd'uiating means conncte'dherewith,means for impressing currents from said transmitting and receiving circuits upon said translating circuitg'whereiby demodulationmaylge eieeted, and the said translating circuit having a reentrant feedba`ok connection between the input and outpit sides` of said amplifying and demodulating means seleetive to a predetermined frequency, whereby the currents of that frequency may be regeneratively amplified-nm In testimony whereof, We have signed our 10 names to this specification this 29th day of September, 1919.

LLOYD ESPENSCHIED. HERMAN A. AFFEL. 

